The present invention relates to roll-type presses for briquetting particulate material. More particularly, it relates to an improved screw feeder for use with briquetting presses of the aforementioned type.
Particulate materials produced by metallic ore beneficiating processes are commonly briquetted prior to shipment to produce a stronger, less porous material that is capable of resisting degradation during handling and is less prone to reoxidize. In roll-type briquetting presses heretofore known in the art, the particles which are typically of -1/16-inch mesh fineness are supplied from a feed hopper to a pair of power driven rolls where compaction occurs. The force necessary to feed the particles to the rolls is provided by a rotary screw feeder that is operative in the hopper. This force must be sufficient in magnitude to overcome the normal rejective forces induced upon the material within the roll nip. For this reason, it is common practice to form the feed hopper with downwardly convergent sides or to provide the feed screw with flights of varying pitch to precompact the material prior to its admission to the roll nip. Precompaction operates to render the feed material more dense on the screw flights and on the inner surface of the hopper adjacent the discharge opening. Such densification is detrimental to feeder operation, especially in the case of machines in which partially reduced iron ore powder is briquetted, in that it can occur to such an extent as to block the slight clearance space that exists between the peripheral edges of the screw flights and the hopper wall thereby preventing any reverse flow of material through this space and the relief that would otherwise be attained thereby. The result of such operating characteristics is the development of excessively high frictional drag forces on the feeder screw with a concomitant increase in power requirements for the screw drive. Moreover, when a comparatively coarse feed material such as pellets or lump ore is used, only a limited feed force can be applied to the screw to protect against jamming due to the poor flow properties of the large particles.
It is toward the improvement of feeder screws for particle briquetting machines, therefore, that the present invention is directed.